On Monday, an NBN Co spokeswoman said the document had not been endorsed by management "due to a number of shortfalls in the methodology and metrics", and had not been verified.

However, she acknowledged some of its findings had merit and had already been adopted in parts of the network rollout where applicable. This included the use of thinner cables and smaller footprint multiport equipment.

Advertisement

"We regularly implement reviews across the network and have not endorsed a 'special project or trial' as suggested by the document and previous reports. Our work in Melton is one example of these ongoing reviews."

"There is no secret project or confidential report. NBN Co has been very public about its intention to deliver fast broadband to 8 million homes and businesses by 2020 and within the $29.5 billion envelope. To do this we must reduce the cost of implementation regardless of technology."

She confirmed the ratio of technologies used in the federal government's preferred multi-technology network design may change as time goes by.

The government-commissioned strategic review recommended a multi-technology design using a combination of fibre to the node and existing copper cables to connect most premises, with the rest connected by satellite, fixed wireless or fibre where applicable.

That design, known as Scenario 6, proposed 26 per cent of fixed-line connection premises would receive fibre to the premises, 44 per cent would receive fibre to the node with copper, and 30 per cent would be connected via HFC (or pay TV cable). Approximately 6 per cent - non fixed-line connections - would use satellite or fixed wireless.

When asked whether NBN would reconsider rolling fibre to more premises and changing the ratios, she said "yes, if it's applicable, absolutely. The ratios will change as we learn more." But added, this did not mean rolling out fibre to everyone.

"We are constantly reviewing and applying new learnings. We don't make an announcement at every step but we do and will apply any improvement to drive efficiencies. Where we can reduce costs without detriment to the customer experience we absolutely will," she said.

"Our job is to continuously review and refine. This time next year we may have come up with another technology," she said, insisting the company was technology-agnostic.

Shara Evans, a telecommunications analyst with Market Clarity who has extensively studied the relative merits of network architectures, was "pragmatic" about the results of the trial but said "if the cost issue were overcome I think it would make sense to roll fibre all the way out."

But inevitable variations during field trials would present their own challenges to any architecture, Ms Evans added.

"Whenever you do price modelling, there's a price model that doesn't reflect the reality of the actual geographies covered by the model. Once you get there, you could find some unexpected surprises. But if the stars line up, I know I would rather have fibre than FTTN."